Allergic diseases are characterized by an overreaction of the immune system to a foreign substance called "allergen". This overreaction occurs when the allergen is ingested, inhaled, injected or is in contact with skin.
About 30% of the population worldwide shows allergic symptoms and approximately 40 - 80% of them suffer from eye symptoms. Allergic diseases that affect the eyes, also called ocular allergies, are a heterogeneous group of diseases that present a wide spectrum of symptoms: redness, itching, burning, pain and even intolerance to light (photophobia). Ocular allergies can manifest both independently and in conjunction with other allergy symptoms such as rhinitis and asthma.
Ocular allergies can be classified into two major categories according to their manifestations. Mild forms such as seasonal allergic conjunctivitis and perennial allergic conjunctivitis belong to the first group. These forms are usually transient and their symptoms appear acutely without affecting the corneal integrity. Vernal keratoconjunctivitis, atopic keratoconjunctivitis and giant papillary conjunctivitis are serious forms of ocular allergies. These forms are usually persistent, chronic and can affect the cornea and, therefore produce lesions affect vision permanently.
Eye allergies usually occur when the conjunctiva (the membrane that covers the eye and lines the eyelid) reacts to an allergen such as pollen, animal hair and dust. The eye, including the conjunctiva, has a high number of mast cells, cells that play a central role in allergy. Mast cells are activated in the presence of allergens and release what is known as mediators of allergy, in a process called degranulation. Allergic mediators activate a lot of responsibility for the typical signs and symptoms of ocular allergy cellular mechanisms. Initially there is what is known as acute phase response or first phase of ocular allergies can progress to a late phase response characterized by the recruitment of inflammatory cells to the site of allergic inflammation and produce a chronic and persistent reaction.
Ocular allergies are one of the most common diseases seen by allergists and ophthalmologists in their consultations. Most of the drugs available for the treatment of ocular allergy are centered in alleviating symptoms in a timely manner.